Effect of ski boot rear stiffness (SBRS) on maximal ACL force during injury prone landing movements in alpine ski racing: A study with a musculoskeletal simulation model

A common anterior cruciate ligament (ACL) injury situation in alpine ski racing is landing back-weighted after a jump. Simulated back-weighted landing situations showed higher ACL-injury risk for increasing ski boot rear stiffness (SBRS) without considering muscles. It is well known that muscle forces affect ACL tensile forces during landing. The purpose of this study is to investigate the effect of different SBRS on the maximal ACL tensile forces during injury prone landings considering muscle forces by a two-dimensional musculoskeletal simulation model. Injury prone situations for ACL-injuries were generated by the musculoskeletal simulation model using measured kinematics of a non-injury situation and the method of Monte Carlo simulation. Subsequently, the SBRS was varied for injury prone landings. The maximal ACL tensile forces and contributing factors to the ACL forces were compared for the different SBRS. In the injury prone landings the maximal ACL tensile forces increased with increasing SBRS. It was found that the higher maximal ACL force was caused by higher forces acting on the tibia by the boot and by higher quadriceps muscle forces both due to the higher SBRS. Practical experience suggested that the reduction of SBRS is not accepted by ski racers due to performance reasons. Thus, preventive measures may concentrate on the reduction of the quadriceps muscle force during impact.     

The evolution of oscillatory behavior during learning on a ski simulator

Recent experiments on the ski simulator produced ambiguous results and raised unanswered questions concerning the true nature of "novice" behavior and the occurrence of behavioral changes during learning. The aim of the present experiment was to analyze the evolving behavior of three beginners during six practice sessions on a ski simulator The position of the apparatus platform was recorded as time series and used for constructing dynamical models, including stiffness and damping functions. The results showed that novices tended to exploit a Rayleigh damping behavior during the first trials and then transition toward a van der Pol damping. These results replicate previous observations by Nourrit, Delignieres, Caillou, Deschamps, and Lauriot (2003) and suggest the transition to the expert behavior could arise early in practice, when the task is of moderate difficulty. The discussion focuses on the properties of the observed learning dynamics and proposes a global conceptualization for acquiring complex motor skills.     

The effect of stud configuration on rotational traction using the studded boot apparatus

Due to its associated injury risk, rotational traction is a frequently measured natural turf surface property. The most commonly used equipment, the studded boot apparatus (SBA), consists of a circular stud configuration that does not replicate the stud pattern on a regular football boot and may under or over estimate the surface traction. The aim of this study was to establish potential differences in the rotational traction measured between the current stud configuration on the SBA and the stud configuration on the most commonly used Australian football boots. The original studded boot had significantly higher rotational traction than the moulded stud sole or bladed sole. Location, quality and time tested all interacted significantly with the rotational traction measured. The current SBA may not accurately represent the rotational traction experienced by football players, and consequently may not be the most appropriate configuration to assess the relationship between rotational traction and injuries.     

Influence of a stressing constraint on stiffness and damping functions of a ski simulator's platform motion

The aim of this study was to assess the effect of stress on a previously acquired motor coordination. Following a longitudinal learning experiment, four participants performed oscillations on a ski simulator, either in normal or stressful conditions. The results showed that the amplitude of the oscillations decreased under stress, but no significant effect was seen regarding coordination, suggesting the strong resistance to stress of overlearned behaviour. Nevertheless, for one participant, a transient regression towards a former stage of learning was observed. This result was consistent with the regression hypothesis formulated by Fuchs (1962).     

体育运动情境再归因训练心理和行为效应研究综述

探讨了在体育运动成就情境中，再归因训练的心理效应和行为效应。分别就体育运动情境再归因训练对学生情绪情感、对随后行为的期望水平及对随后行为坚持性的影响进行综述。并且对如何在体育教学中实施再归因训练提出了具体的方法措施。     

Influence of a stressing constraint on stiffness and damping functions of a ski simulator's platform motion

The aim of this study was to assess the effect of stress on a previously acquired motor coordination. Following a longitudinal learning experiment, four participants performed oscillations on a ski simulator, either in normal or stressful conditions. The results showed that the amplitude of the oscillations decreased under stress, but no significant effect was seen regarding coordination, suggesting the strong resistance to stress of overlearned behaviour. Nevertheless, for one participant, a transient regression towards a former stage of learning was observed. This result was consistent with the regression hypothesis formulated by Fuchs ().     

沈阳市滑雪场经营困境与发展对策研究

通过对沈阳市滑雪场经营现状的研究,指出了滑雪场的经营困境:配套设施不完善,未形成统一的产业链;基础设施建设不够完善,经营种类单一;雪场收费标准过高,影响了大众旅游;服务质量不高,亟待改善服务质量;面临非雪期经营难题,安全保障不健全等。针对这些经营困境提出了发展对策,旨在为滑雪场实现快速健康经营提供参考依据。     

The effect of sex and localised fatigue on triceps surae musculoarticular stiffness

Purpose: The main purpose of this study was to investigate the influence of fatigue on musculoarticular stiffness (MAS) of the ankle joint across sexes. Methods: Twenty-seven males and 26 females participated in the study. After baseline assessment of MAS and related variables, localised fatigue was induced in triceps surae using the standing heel-rise test during which the subjects were instructed to lift and drop the heel at a frequency of 0.5?Hz. When subjects were unable to continue due to exhaustion the test was terminated and another MAS test was performed soon after. Results: Significant higher triceps surae MAS was found in men compared to women (p?p??1 and from 14.5 to 13.9?KN?m^?1 in men and women, respectively. Percentage changes revealed, however, that in relative terms the changes in all the variables evaluated were similar (p?>?.01) between sexes, with MAS less than 5%. Conclusion: Despite the sex-related differences at baseline, fatigue seems to affect biomechanical properties of the ankle joint similarly in men and women.     

The effect of short-term isometric training on core/torso stiffness

“Core” exercise is a basic part of many physical training regimens with goals ranging from rehabilitation of spine and knee injuries to improving athletic performance. Core stiffness has been proposed to perform several functions including reducing pain by minimising joint micro-movements, and enhancing strength and speed performance. This study probes the links between a training approach and immediate but temporary changes in stiffness. Passive and active stiffness was measured on 24 participants; 12 having little to no experience in core training (inexperienced), and the other 12 being athletes experienced to core training methods; before and after a 15 min bout of isometric core exercises. Passive stiffness was assessed on a “frictionless” bending apparatus and active stiffness assessed via a quick release mechanism. Short-term isometric core training increased passive and active stiffness in most directions for both inexperienced and experienced participants, passive left lateral bend among experienced participants being the exception (P < 0.05). There was no difference between the inexperienced and experienced groups. The results confirm that the specific isometric training exercise approach tested here can induce immediate changes in core stiffness, in this case following a single session. This may influence performance and injury resilience for a brief period.     

The effect of torsional shoe sole stiffness on knee moment and gross efficiency in cycling

Altering torsional stiffness of cycling shoe soles may be a novel approach to reducing knee joint moments and overuse injuries during cycling. We set out to determine if the magnitude of three-dimensional knee moments were different between cycling shoe soles with different torsional stiffnesses. Eight trained male cyclists cycled at 90% lactate threshold power output in one of two cycling shoe conditions in a randomized crossover design. The shoe sole was considered torsionally flexible (FLEX) compared to a relatively stiffer (STIFF) sole. Gross efficiency (GE) and knee joint moments were quantified. No significant effect of shoe condition was seen in GE (21.4 ± 1.1% and 20.9 ± 1.6% for FLEX and STIFF, respectively, P = 0.12), nor in three-dimensional knee moments. 4 of the 8 subjects had reduced knee moments in at least 2 of the 3 moment directions. These “responders” were significantly shorter (1.73 ± 0.02 m vs 1.81 ± 0.04 m, P = 0.017) and had a higher relative maximal aerobic power (MAP) (4.6 ± 0.3 W?kg-1 vs 3.9 ± 0.3 W?kg-1, P = 0.024) compared to non-responders. These results suggest that certain shoe characteristics may influence certain individuals differently because these participants belong to different “functional groups”; certain individuals may respond positively to FLEX, while others may not. Further studies should test this proposed hypothesis.     

The influence of golf shaft stiffness on grip and clubhead kinematics

The purpose of this study was to investigate the influence of shaft stiffness on grip and clubhead kinematics. Two driver shafts with disparate levels of stiffness, but very similar inertial properties, were tested by 33 golfers representing a range of abilities. Shaft deflection data as well as grip and clubhead kinematics were collected from 14 swings, with each shaft, for each golfer using an optical motion capture system. The more flexible shaft (R-Flex) demonstrated a higher contribution to clubhead speed from shaft deflection dynamics (P < .001), but was also associated with significantly less grip angular velocity at impact (P = .001), resulting in no significant difference in clubhead speed (P = .14). However, at the individual level, half of the participants demonstrated a significant difference in clubhead speed between shafts. The more flexible shaft was also associated with significantly different magnitudes of head rotation relative to the grip. More specifically, both bend loft (P < .001) and bend lie (P < .001) were greater for the R-Flex shaft, while bend close (P = .017) was greater for the stiffer (X-Flex) shaft. However, changes in grip orientation resulted in no significant differences in face orientation, between the shafts, at impact.     

The effect of caffeine ingestion on 8 km run performance in a field setting

The aim of this study was to assess the effect of caffeine ingestion on 8 km run performance using an ecologically valid test protocol. A randomized double-blind crossover study was conducted involving eight male distance runners. The participants ran an 8 km race 1 h after ingesting a placebo capsule, a caffeine capsule (3 mg x kg(-1) body mass) or no supplement. Heart rate was recorded at 5 s intervals throughout the race. Blood lactate concentration and ratings of perceived exertion were recorded after exercise. A repeated-measures analysis of variance (ANOVA) identified a significant treatment effect for 8 km performance time (P < 0.05); caffeine resulted in a mean improvement of 23.8 s (95% confidence interval [CI] = 13.1 to 34.5 s) in 8 km performance time (1.2% improvement, 95% CI = 0.7 to 1.8%). In addition, a two-way (time x condition) repeated-measures ANOVA identified a significantly higher blood lactate concentration 3 min after exercise during the caffeine trial (P < 0.05). We conclude that ingestion of 3 mg . kg(-1) body mass of caffeine can improve absolute 8 km run performance in an ecologically valid race setting.     

Biomechanics of the ski cross start indoors on a customised training ramp and outdoors on snow

An effective start enhances an athlete's chances of success in ski cross competitions. Accordingly, this study was designed to investigate the biomechanics of start techniques used by elite athletes and assess the influence of different start environments. Seven elite ski cross athletes performed starts indoors on a custom-built ramp; six of these also performed starts on an outdoor slope. Horizontal and vertical forces were measured by force transducers located in the handles of the start gate and a 12-camera motion capture system allowed monitoring of the sagittal knee, hip, shoulder, and elbow kinematics. The starting movement involved Pre, Pull, and Push phases. Significant differences between body sides were observed for peak vertical and resultant forces, resultant impulse, and peak angular velocity of the shoulder joint. Significantly lower peak vertical forces (44 N), higher resultant impulse (0.114 Ns/kg), and knee joint range of motion (12°) were observed indoors. Although movement in the ski cross start is generally symmetrical, asymmetric patterns of force were observed among the athletes. Two different movement strategies, i.e. pronounced hip extension or more accentuated elbow flexion, were utilised in the Pull phase. The patterns of force and movement during the indoor and outdoor starts were similar.     

谈中国高山滑雪的现状和整改措施

对中国高山滑雪的现状进行分析,并具体地提出了一系列整改措施,旨在找出差距、改善高山滑雪现状,提高全民普及率,尽早提高专业队整体素质.     

高山滑雪多媒体网络课件制作与应用

介绍了高山滑雪多媒体网络课件设计思想和具体的制作过程,阐述了网页界面、素材收集、分横块设计等观点,对课件内容的制作做了全面的描述.对脚本的制作、素材制作、课件网上发布等,给出了一个完整的多媒体网络课件总体设计和制作的蓝图.     

The effect of acute aerobic exercise on central arterial stiffness,wave reflections,and hemodynamics in adults with diabetes: A randomized cross-over design

BackgroundIndividuals with diabetes have greater central arterial stiffness, wave reflections, and hemodynamics, all of which promote the accelerated cardiovascular pathology seen in this population. Acute aerobic exercise has been shown to be an effective strategy for reducing central arterial stiffness, wave reflections, and hemodynamics in healthy individuals; however, the effects of acute aerobic exercise in reducing these outcomes is not well established in people with diabetes. Recently, implementation of high-intensity interval exercise (HIIE) has shown superior improvements in cardiovascular health outcomes when compared to traditional aerobic exercise. Yet, the effect of HIIE on the aforementioned outcomes in people with diabetes is not known. The purpose of this study was to (i) describe the central arterial stiffness, wave reflections, and hemodynamic responses to a bout of HIIE and moderate-intensity continuous exercise (MICE) in adults with diabetes; and (ii) compare the effects of HIIE and MICE on the aforementioned outcomes.MethodsA total of 24 adult men and women (aged 29–59 years old) with type 1 (n = 12) and type 2 (n = 12) diabetes participated in a randomized cross-over study. All participants completed the following protocols: (i) HIIE: cycling for 4 × 4 min at 85%–95% of heart rate peak (HR_peak), interspersed with 3 min of active recovery at 60%–70%HR_peak; (ii) MICE: 33 min of continuous cycling at 60%–70%HR_peak; and (iii) control (CON): lying quietly in a supine position for 30 min.ResultsA significant group × time effect was found for changes in central systolic blood pressure (F = 3.20, p = 0.01) with a transient reduction for the HIIE group but not for the MICE or CON groups. There was a significant group × time effect for changes in augmentation index at a heart rate of 75 beats/min (F = 2.32, p = 0.04) with a decrease following for HIIE and MICE but not for CON. For all other measures of central arterial stiffness and hemodynamics, no significant changes were observed (p > 0.05).ConclusionA bout of HIIE appears to lead to a greater transient reduction in central systolic blood pressure than the reduction observed following MICE; however, both HIIE and MICE improved augmentation index at a heart rate of 75 beats/min in people with diabetes. There was no significant difference in response to HIIE and MICE in all outcomes. This provides preliminary evidence on the role of HIIE on such outcomes in people with diabetes.     

Effect of sex and fatigue on muscle stiffness and musculoarticular stiffness of the knee joint in a young active population

The purpose of this study was to investigate the influence of sex and fatigue on knee extensor peak torque (PT), muscle stiffness (MS) of the vastus lateralis (VL) and knee joint musculoarticular stiffness (MAS) in young adults. Twenty-two male and 22 female recreational athletes participated. Males were characterised by higher relaxed [pre-: males 364.43 (52.00) N · m^–1, females 270.27 (37.25) N · m^–1; post-: males 446.75 (83.27) N · m^–1, females 307.39 (38.58) N · m^–1] and contracted [pre-: males 495.07 (71.04) N · m^–1, females 332.34 (85.42) N · m^–1; post-: males 546.37 (90.74) N · m^–1, females 349.21 (85.55) N · m^–1] MS of the VL, and knee joint MAS [pre-: males 1450.11 (507.98) N · m^–1, females 1027.99 (227.33) N · m^–1; post-: males 1345.81 (404.90) N · m^–1, females 952.78 (192.38) N · m^–1] than females pre- and post-fatigue. A similar finding was observed in pre-fatigue normalised knee extensor PT [pre-: males 2.77 (0.42) N · m kg^–1, females 2.41 (0.40) N · m kg^–1, post-: males 2.53 (0.54) N · m kg^–1, females 2.26 (0.44) N · m kg^–1]. After the fatigue protocol, normalised knee extensor PT and knee joint MAS decreased, whilst relaxed and contracted MS of the VL increased in both sexes. These observed differences may contribute to the higher risk of knee injury in females and following the onset of fatigue.     

The influence of golf club shaft stiffness on clubhead kinematics at ball impact

The role of shaft stiffness on the golf swing is not well understood. Studies in which golfers hit balls with clubs of varying shaft flex have reported changes in ball distance. The results of mathematical models suggest that shaft stiffness affects only the orientation of the clubhead at impact, not the speed of the clubhead, but there are no experimental results validating these findings. The purpose of this study was therefore to experimentally examine the influence of shaft stiffness on clubhead kinematics at ball impact. Forty golfers hit 10 balls with each of five drivers varying in shaft stiffness from 'Ladies' to 'Extra-Stiff', in a double-blind study design. The motions of three reflective markers attached to the clubhead were captured with a high-speed motion analysis system. At ball impact, shaft stiffness had a statistically significant influence on clubhead speed for 27 subjects, on loft angle for 11 subjects, and on lie angle for all 40 subjects. No effect was observed on face angle, in to out path angle, or attack angle. These results show that shaft stiffness can affect ball launch conditions by altering clubhead speed and/or loft angle.